In the art of zeolites, zeolite with a composite pore structure means that the zeolite has incorporated a further pore structure beyond its original pore structure so that to have a composite pore structure, thereby the zeolite has varied pore structure and improved porosity as well as varied mass transfer ability and catalytic activity.
Since MCM-41 zeolite molecular sieve with a composite pore structure was synthesized by Mobil Company from USA in 1992 and the same was found to be with an ability of quickly mass transferring and high catalytic activity for hydrocarbon conversions [cf. Kresge, C. T., Leonovicz, M. E., Roth, W., J., Vartuli, J. S. Nature 353, (1992), 710.], the zeolite with a composite pore structure has received more and more attention and there are more and more zeolites being imparted with composite pore structures successfully, thereby zeolites being imparted with more possibility for extensive industrial uses.
Zeolite beta with a composite pore structure is such a zeolite, whereinto a meso-pore structure is incorporated beyond its original micro-pore structure, so that zeolite beta has a composite pore structure comprising both micro-pore structure and meso-pore structure simultaneously, thereby zeolite beta has improved mass transfer efficiency and catalytic activity for hydrocarbon conversions.
Ryoo et al. have developed a bifunctional surfactant for synthesizing zeolite comprising both mesopore and micropore simultaneously, thereby yielding zeolite nanosheets or mesoporous zeolites. However, said bifunctional surfactant is costly so that its industrial applications are less feasible. Thus, there is still need to improve the synthesis of zeolite beta with a composite pore structure in the art.
In order to make zeolite beta with a composite pore structure could be used commercially, in Chinese patent application CN 1749162A, the present inventors have successfully synthesized zeolite beta with a composite pore structure by using a combination of polyquaternium-6 (polydiallyldimethylammonium chloride) and TEAOH (tetraethylammonium hydroxide) as templates (cf. example 2 and FIGS. 8-9 therein).
According to such a synthesis route, based on the conventional concepts in the art, of the combined templates, the organic small molecular template, i.e. tetraethylammonium hydroxide (TEAOH), is used to form the microporosity, and the organic high molecular template, i.e. polyquaternium-6, is used to form the mesoporosity. Thus, the two organic templates have to match with each other very well, otherwise, some amorphous porous materials could be easily formed in the synthesized zeolite. Thus, such combined templates make the synthesis of zeolite beta with a composite pore structure little complicated, although the same had been more feasible than that by Ryoo et al. for commercial applications already.
With such a situation, the present inventors now have surprisingly found that zeolite beta with beneficial properties, more specifically zeolite beta having a composite pore structure, can be successfully synthesized by using a polymeric compound comprising ionizable polydiallyldimethylammonium (PDADMA) cation such as polyquaternium-6 as the only template present during its preparation. Viewing that such a polymeric compound such as polyquaternium-6 is much cheaper than TEAOH as commercial agents, the present invention makes the synthesis of zeolite beta with a composite pore structure more simplified with reduced cost, thus, promoting zeolite beta with a composite pore structure to be used in extensive industrial applications.